Effective in reducing volume of BGA package products, a window ball grid array (window BGA) package is in line with the electronic product trend toward miniaturization. A window BGA package has the following characteristics: first, installed in a substrate for carrying a semiconductor chip is at least one cavity penetrating the substrate, and as a result, not only is the semiconductor chip mounted on the upper substrate surface in a face down manner, but one end of the cavity is closed; second, solder wires made from a certain material, for example, gold, are inserted into the cavity to electrically connect the semiconductor chip and electrically connecting pads beneath the substrate; thirdly, the semiconductor chip is electrically connected to an external printed circuit board by means of solder balls installed on the lower substrate surface and functioning as input and output leads; fourthly, the electrically connecting pads, installed on the lower surface of the substrate and connected to the semiconductor chip by the solder wires, are distributed on the periphery of the cavity; fifthly, a nickel/gold layer is formed on the surfaces of the electrically connecting pads such that during a wire bonding operation electrical coupling of the gold wires and the electrically connecting pads is achieved because both of them are fabricated from the same metal, i.e. gold; lastly, given the aforesaid technology, extrinsically induced oxidation of the body of the electrically connecting pads, typically oxidation of copper, is prevented.
Manufacturers nowadays usually form a nickel/gold metal protecting layer on the aforesaid electrically connecting pads, using an electroplating process. Correspondingly, it is necessary to lay a plurality of plating wires in a substrate, wherein the plating wires are connected to the electrically connecting pads such that during the electroplating process the plating wires function as electrical conduction paths, to lay a nickel/gold metal protecting layer on the electrically connecting pads by electroplating. Afterward, the substrate on which the nickel/gold process is performed and finalized proceeds to a router process whereby, not only is the electrical connection between the plating wires and the electrically connecting pads severed, but a cavity is formed in the circuit board.
Referring to FIGS. 1A through 1C, which are flow diagrams showing a window BGA package circuit board undergoing a nickel/gold process and an opening process successively according to the conventional technology.
Referring to FIGS. 1A, 1B, wherein a circuit board 1 with a circuit layer 11 formed on at least one surface thereof is prepared. The circuit board 1 has already finished undergoing a pre-process. At least one selected zone S (as shown in FIG. 1B) intended for subsequent formation of an opening is defined on the circuit board 1. The circuit layer 11 comprises a plurality of electrically connecting pads 110 and plating wires 111 connected to the electrically connecting pads 110. A metal protecting layer 112 is formed to coat both the electrically connecting pads 110 and the plating wires 111. A solder mask layer 113 is further formed on the surfaces of the circuit board 1; formed in the solder mask layer 113 is an opening 113a to expose the electrically connecting pads 110 and the plating wires 111, both covered in the metal protecting layer 112.
Referring to FIG. 1C, a router process is carried out, using a milling cutter, wherein the periphery of the selected zone S is cut with the milling cutter to achieve two purposes. First, the electrical connection between the plating wires 111 and the electrically connecting pads 110 is severed, to build an open circuit. Second, the selected zone S is removed, and a thru-hole-like cavity 12 is formed in the circuit board, to fabricate a window BGA package circuit board 1′.
Since both the plating wires 111 and the metal protecting layer 112 are made from ductile, malleable materials, burrs (symbol b) appear on the periphery of the cavity 12 in the window BGA package circuit board (as shown in FIG. 1C) when the ductile, malleable metal protecting layer material is pulled out with a milling cutter in the course of cavity 12 cutting and forming.
Although some manufacturers attempted to solve the aforesaid problem with burrs by cutting them, using milling cutters exclusively used in a router process, their endeavors prove ineffective, as the burrs survive the cutting process. Furthermore, as regards the fabrication process, its yield and throughput are low, due to the ineffective router process which, in turn, occurs because window slot pitches remain wide.
Accordingly, an issue that currently needs urgent solution involves overcoming the drawbacks of the aforementioned prior art for manufacturing semiconductor package circuit boards, that is, low yield and low throughput attributable to the burrs produced in the course of the cutting of plating wires with milling cutters.